7/25/11 Atomic Structure  The atom is composed of protons, neutrons, and electrons  In a neutral atom, the number of electrons and protons are equal  The number of protons identified the element  This is the atomic number and is given the symbol “Z”  The number of protons + the number of neutrons are essentially responsible for the mass (amu) of the atom

7/25/11

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7/25/11 The Fundamental Particles  Atomic number: Z  Number of protons in the nucleus of an atom. All atoms of the same element have the same number of protons  Atomic mass number: A  Number of protons and neutrons in the nucleus of an atom  Isotopes  Atoms of the same element with the same number of protons but different numbers of neutrons